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Why are Vertical tails generally tapered?
I'm just intrigued to know why the vertical tail of a majority of aircraft is tapered? Is it due to aerodynamics, structural design or due to some instrumentation or multiple other reasons?

There are obvioius aerodynamic and structural advantages for taper (and sweep), but also remember that a signficant factor in a vertical tail's shape is what comes down to... styling.  The fin and rudder form maybe a third of the airplane's shape in profile and the "look" that defines it.  Designers aren't machines; they are humans with a sense of aesthetics like anybody else, and there is a bit of art to it, and one of the great things about aviation is artistic forms flow naturally from efficient shapes, like teardrops and tapered and swept surfaces.  Any designer will consider the look as part of the overall shape of the tail to some degree or another.
Now, the Pilatus Porter uses a constant chord vertical tail and it works perfectly fine and is cheaper and simpler to build and in most light low speed airplanes that is a more important factor than the aerodynamic ones.  But it looks incredibly ugly, and who the hell wants to build something ugly unless you've decided to make that part of your brand, or you don't care about the look at all, or the plane was designed by a committee with no sense of aesthetics.
Since the 50s, on GA aircraft, sweep became associated with "modern" and high performance, since on high performance aircraft that was actually true.
Between 1950 and 1966, Cessna's tails went from:

and it made not the slightest difference in the airplanes' handling or performance.  It was strictly for looks.  From a manufacturing and aerodynamic perspective, they should have stuck with the middle square tapered one used from the mid 50s to the early 60s, but in the  mid 60s swept tails were all the rage in GA.

I really think the middle looks better than the swept one anyway!

Same here I always preferred Cessna's razor back square tails like the 180 and early 150s and 172s.

The vertical tail and the horizontal tail are wings, and follow the same construction rules. The span-wise lift distribution is much better if the wing is tapered: more lift at the root, less at the tip.

The wing can be built lighter, root area is larger, torsion stiffness is higher.
Vortex induced drag is lower.

As a reference, from Torenbeek: pages 232 & 233

It is observed that nowadays there are basically three forms of straight wings: the tapered wing, the untapered (rectangular) wing and the wing with a prismatic inner portion and a tapered outboard portion.

About taper for wings (and for tail surfaces):

Tapered wings have been adopted for the majority of aircraft since they offer an efficient solution on account of their low induced drag, high maximum lift, low structural weight...(and) acceptable stalling characteristics can be obtained, provided the wing is not too sharply tapered.

Untapered wings are inferior and cheap:

The untapered wing is attractive from the point of view of manufacture, since only one airfoil contour is involved; this simplifies jigging as there are no compound curvatures. It is aerodynamically inferior to the tapered wing, but may nevertheless be the logical choice for inexpensive private aircraft, where the utilization factor is low and initial cost and cheapness of components are important.

Don't forget styling.  The tail shape is one an aircraft's most defining features.  Lots of airplanes use constant chord horizontal tails (Twin Otter for example) but always have some taper to the vertical one, swept or not, because a constant chord rectangular vertical tail looks like hell (e.g., Pilatus Porter).

@JohnK There are genuine constructive and aerodynamic reasons for tapering wings and tails. I’ll leave styling as anybody’s opinion.

@JohnK, yet there are counterexamples... :)

Look at what they added to the front of the "prismatic" (dashed line).

And we can round off the edges to make it look better.

A little quandary here (again thanks for John's artwork) for the designer:
Earliest tail Pros - very strong with desirable Prandtl style trailing edge and swept forward edge, low aspect ratio and high stall AOA.  No accident this was the tail of the Bf 109.  Cons -
 not as effective at generating lift as a straight wing (ASE readers should be seeing this trend), lots of area for cross wind "weather vaning".  The fillet seen in the P 51 would also improve high AOA lift.
Squarish tail Pros - again, very strong, low aspect ratio, high stall AOA.  Reliable and easy to make.  Cons - not as effective in lifting, there for needs to be bigger (drag, weather vaning).
Swept wing tail Pros - Stylish, better spanwise load distribution (thanks Peter), more efficient at generating lift (same lift for smaller size).  Less weather vaning.  Cons - will stall at a lower AOA, and because of its greater length, is not nearly as strong.  This is why airline pilots cannot rudder aggressively, particularly at high speeds. It will break.
So, aerodynamicly, the tapered tail gets a plus for looks and lifting efficiency, but a minus for strength and high AOA performance.  The first two, particularly the earliest one, may be a better pick, particularly for aerobatics.

I think having a tapered tail increases its torsional stiffness and hence would have better structural strength when compared to rectangular tails. Isn't this generally the case? or am I missing any detail here?

@CuthillMckee You're absolutely right, that is generally the case.

@CuthillMckee tapering the shape lessens the effect of the wind by moving load center closer to the root, modern windmills are a good example of this.  But when you "taper", you have less working area.  For a given torsional stiffness, square is better than rectangle, tapered better than straight.  You can improve TS with better design and materials, but the shape relationships hold.


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Is the location of an aircraft spoiler really that vital?
I was wondering that spoilers in most of the aircraft are always placed aft (towards the tail) the CG location. Why aren't they placed ahead of the wings or near the nose of the aircraft? The same is the case with parachutes. For small UAVs, the parachutes are either at the CG location or placed behind it. Is there a really strong design point to this method? Any suggestions/information would be appreciated?

How would you place spoilers ahead of the wing? Are you proposing something like "spoiling slats" or "spoiler canards"? Their purpose is to disrupt the airflow over the top of the airfoil and stall it, which is why they're normally integrated into the top surface of the wing.

I think you may be confusing spoilers and air brakes. A spoiler is a movable control surface, typically on the upper surface of the wing, intended to disturb airflow over the wing in order to reduce the lift generated by the wing. An air brake (or speed break) is a device, often implemented as a section of the rear fuselage which can be pushed open by hydraulics to create drag in order to slow the aircraft in flight.

Surfaces sticking out ahead of the Centre of Gravity act in an unstabilising manner: any dissymmetry will want to amplify itself. A dart thrown with the feathers first is in an unstable equilibrium and will very quickly turn around 180º.
Surfaces behind the CoG act as stabilisers, keeping the nose pointing forward. An aeroplane has vertical and horizontal tail surfaces at the back just for this purpose. When spoilers are deployed at low speeds, the aeroplane is in a situation where you don't want any destabilising moments.
Aerodynamic behaviour is stable if a disturbance auto-corrects: a deviation is automatically blown back. Since motion in flight is relative to the Centre of Gravity, it follows that the aerodynamic Centre of Pressure must be behind the CoG.

Thanks for the input. Is there a way to numerically compute such effects for preliminary quantitative understanding?

There is most definitely a way, but it's a multidimensional matrix with lots of inputs and outputs. In case of a dart or a lifting body without wings, the fuselage just wants to turn perpendicular to the airflow with a certain torque, and the stabilising surface must be large enough to compensate for this. Presence of a wing complicates the matrix: a roll attitude causes a yawing moment, a yawing moment causes a rolling moment and a whole lot more cross-couplings.

For the spoiler, if it is placed behind the aerodynamic centre of the aeroplane it should usually be OK, but there does need to be an analysis to see if actuator failure on one side can still be compensated for by the vertical tail etc.

@CuthillMckee - a crude way to compute the effect is to calculate the area of a surface, multiplied by it's distance from the centre of gravity. Generally there will be about 10 times as much behind the CG as in front. Unless you've got a computer model, draw a grid over the plan (or side) view of the plane and count squares in each column. You can assume that the CG is 25-30% from the front of the average wing chord. Also, are we talking about air-brakes? Spoilers are usually on the top surface of the wing.

Same thing with both Arrows and firework rockets. The latter really emphasises that drag has a really big effect, without the apparently obvious effect of the fletch/vane of an arrow/dart.

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B767 antenna identification

Can anyone identify which comms/nav system the circled antenna belongs to?
Thanks.

I‘d have to double check, but I believe it’s a drain mast rather than an antenna.

That is one of two heated drain masts for the lavatory sinks.

How does the drainage of the gray water work?

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What are the pros and cons of PPL training at class C airport?
I'm looking to start PPL training soon, and the closest airfield is Austin-Bergstrom International, which is a class C. The only downside I see to doing training at KAUS is that the few PPL programs there has planes no smaller than 172's, which is 15% more costly than the alternative PA-38 at an airfield 30 miles north, or marginally cheaper 172's 30 miles south in San Marcos. Instructor rates are roughly equal. 150/2's don't seem to exist around here.
So the question is, are there advantages to training in a class C that make up for the cost difference? What disadvantages do you foresee?
Thanks.

Other than being more comfortable with ATC, there really is none. There are pros and cons on both sides.

The question isn't asking "which is better," which would be asking for opinions; it asks for a statement of the advantages & disadvantages, which is answerable with objective factors. While different pilots may hold differing opinions if training at a Class C airport is a better option, they can probably agree on the factors involved: more congestion, more exposure to ATC, longer taxi routes, wide vs narrow runways, etc. Voting to keep open.

Being more comfortable with ATC at the primary training stage is a huge advantage for a pilot, IMO.

The only obvious advantage is less travel time.  Whether being comfortable with ATC is much of an advantage depends on where you intend to do most of your flying.  And the disadvantage is that the cost might be more (even if hourly rates are the same) since at a busy airport you'll spend more time waiting for other traffic.

A possible disadvantage is getting TOO used to ATC services, to the point where you might forget etiquette (and safety) when flying into an uncontrolled airport. In other words, don't forget your due diligence of saying who you are, where you are, and what your plan is, at an uncontrolled airport, simply because there's no tower to call.


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What forces act on an airplane's door from the outside in cruise?
The inside cabin pressure from what I understand is pressurized to the values found at 6000-8000 feet high (11.34 psi at 7000 feet), at which point we can find the amount of force can be found acting against the door internally.
What about the pressures outside of the door? Is it just the pressure of the altitude of the plane acting against the door, or are there other forces involved, such as the force of the wind?

If you are talking about passenger doors, their surface will be mostly parallel to the direction of motion, so the wind will not act directly on them (otherwise the aircraft would be in a sideslip, with the drag and fuel consumption greatly increased).
So yes, you can assume only the external pressure is acting on them (plus gravity).
The pressure will generally not be the nominal value, given the fact that the turbulence near the surface of the airplane slightly disturbs it, but neglecting this effect is a good first approximation.

Yes, I mean the main door that you enter/exit a plane on. But regarding the wind, even if the flow of the wind is parallel to the door, isn't the door still receiving some fraction of the wind force?
Would the mechanics of the door and the interior pressure have any effect if one were to attempt to open the door from the outside?

"isn't the door still receiving some fraction of the wind force?" well, that depends on the model you are considering and the degree of approximation you are interested in. "Would the mechanics of the door and the interior pressure have any effect if one were to attempt to open the door from the outside?" that's a different question.

@Federico Maybe that’s what this guy would like to know

A door that is, say, 36" x 80" (0.9m x 2m), with a surface area of 2880 sq/in (1.8m2), at 8 psi (55kPa) max cabin pressure differential, which most airliners run at, will have roughly 12 tons (102kN) acting on the perimeter fittings trying to blow it out. Any other forces acting on it are microscopic in comparison.
For non plug type doors that depend on bayonet latch pins, the shear loads on the pins are such that it is impossible to move the latching mechanism.  If superman was able to move the operating lever, it may or may not just bend the linkage, but no human will be able to move it.
For a plug door of the dimensions above, it has to move inboard to start to open it, so you would have to be able to apply 12 tons of pull force to unplug it.
Just the acrylic cabin windows are holding back over half a ton each when you are cruising along at 38000 ft.
This is why you don't have to worry about a crazy person trying to open a window escape hatch in flight.

I may have misread the question, but it appears that the OP is asking about the ambient pressure outside the door, which is certainly not zero.  Would the outside air pressure be truly negligible, or would it reduce the net force on the door by a measurable amount?  (I'm sure your conclusions are correct, but is it 12 tons or 10?)

@ymb1 I agree, but I don't see an indication in the answer that the pressures are differential vs. absolute.  Maybe I'm just being under caffeinated/ overly pedantic.

@DanPichelman The answer literally says " 8 psi (55kPa) max cabin pressure differential," (emphasis mine) in the first sentence.

@Polygnome Thanks.  I clearly misread the answer.  My bad.

8 psi is typical of airliners to deliver an 8000 foot cabin at cruising altitude.   Turbo props that are limited to the mid 20s are generally around 5 psi.  I believe the 777 is certified to 10 psi if I recall, which gives about a 6000 ft cabin at altitude, so you can imagine the forces in its doors and windows.

I'm glad you included the amount of pressure on the windows... I was already going the other direction, imagining how much pressure must be on the entire interior of the airframe, if there is 12 tons just on the door...

Well for the fuselage itself it's converted to a tensile load distributed through the aluminum skin itself and is pretty low as long as the stress isn't allowed to concentrate too much at one spot.  For windows there will be a stress concentration at each fastener, but there are a lot of them so that 1000 lbs is maybe 20 or 30 lbs at each screw and acrylic is pretty strong stuff.  A main door with 8 latch pins or plug pads has the force concentrated there, but you're talking one or two thousand pounds on each fitting that's made of material that can take many times that.  Not so bad really.

@DanPichelman
Yes, I'm asking about the pressures outside of the plane acting outside of the door, as well as the different gravity acting on the door at standard altitude, and any wind force present.

If the door was at the forward end where the taper of the fuselage was presenting the door to the airflow at an angle, there would be some dynamic force opposing the pressurization loads trying to blow the door out, but these forces would be a small fraction of the blow out force.  If the door is along the side parallel to the airstream, any dynamic force from the airstream would be close to zero as the pressure along the straight side of the fuselage away from the wings is roughly ambient (that's where the static ports are).  Not sure what you mean by gravity.


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Why didn't NWA 85 request/receive fighter jet help with their mysterious rudder failure?
I recently watched a documentary about the Northwest Airlines Flight 85. The flight experienced a grave rudder malfunction when it was over the Bering Sea and had to turn back for an emergency landing in Anchorage, from which it was about two hours away.
The captain has been quoted:

I would have given a thousand dollars for a rearview mirror. The self-diagnostics of the airplane which normally are pretty good, in this case basically told us nothing. And the control position indicator was really the only indication that we had had that the rudder was malfunctioning. The tail could be coming apart for all we knew. And if it came apart, we probably would lose the airplane...We were just going to have to figure this out.

So, they had something wrong with their rudder, but couldn't figure it out. Wouldn't it have helped if they had the pilot of another plane come and see it?
Since they were heading for Anchorage, couldn't they or the air traffic control have called the Elmendorf Air Force Base and asked for a fighter jet to come and see the rudder of the Boeing 747-400? There would have been plenty of time, since they were some two hours away from Anchorage. You'd also think that each Air Force base has a fighter jet that's able to get to air at a moment's notice. A jet would've easily been able to meet them in the middle and take some photos of the rudder.
There were some 400 people aboard the NWA flight, so it's not like it was a minor issue. For all anyone knew, the plane could've crashed into the ocean at any moment. At least a fighter jet pilot would've been able to pinpoint the exact crash site for a search party later on. What am I missing?

By the time they got a fighter there they had already figured out how to fly the airplane so somebody looking at it wouldn't have given them any additional information, what was to gain there?

@RonBeyer, For all anyone knew, the plane could've crashed into the ocean at any moment. At least a fighter jet pilot would've been able to pinpoint the exact crash site for a search party later on. Also, I'm pretty sure fighter jets have been called to escort planes for lesser reasons too.

@ZeroOne By the time the fighter would have got to them, they'd either have the situation under control or be long in the water, they were that far out. Those fighters would have needed tanker support to get to them too.

@jwenting I don't think so. In the article that I linked to, the captain says that "We were about an hour and forty minutes west of Anchorage, about 500 miles.". That's some time after the incident started. According to Wikipedia, the range of an F-22 Raptor is 1840 miles, more than enough for a trip to the NWA 85 and back.

Dispatching a very expensive fighter to intercept the airliner would have been useless. A fancy rearview mirror? If the damage was as bad as the captain thought it could be the fighter would not be able to do a thing about it. They figured it out. Also, pinpointing crash sites is the job of EPIRB's, not F22's.


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After hernia surgery, what do I need to do to be cleared to exercise the privileges of my PPL?
After hernia surgery, what do I need to do to be cleared to exercise the privileges of my PPL?
I recently had hernia surgery in the past few weeks and just had my follow-up appointment with my surgeon yesterday. A week or so ago, I called the FAA Medical Hotline to self-report on my condition and was told that I was grounded until I received a doctor's notice clearing me for normal activity.
The research I've done shows that I need to submit a doctor's letter and an operative report to the FAA to be considered medically eligible again.  My doctor's notice from my recent appointment says that I am cleared to return to normal activity on 1/31/20. Is this sufficient for the FAA to clear my grounded status?

As a general rule, your AME is much better placed to advise you on this than random internet people.

+1 on Jamiec's comment.  Beyond that, in the last paragraph you say you have done the research.  I doubt many would refute you, so why don't you just send your doctor's note to the FAA and be done with it?  If you really want an answer before sending it, call the same FAA hotline and ask to speak with the guy who grounded you.

@MichaelHall I think the poster misunderstood the person on the hotline. The FAA didn’t ground him; they can’t do that without some kind of formal action. What the FAA told him is that pursuant to the FARs he was supposed to self-ground until he was cleared by his doctor. i.e. had no “medical condition that would make you unable to meed the requirements of the medical certificate.”

@JScarry, I agree, I was mainly suggesting that he close the loop with the folks he spoke with just in case they made any comments in his record regarding the expectation of a note clearing him again.

What makes you think you need to inform the FAA of your status? I know of no rule that requires notifying the FAA until you go for your next medical. The FAA has a list of disqualifying medical conditions, and hernias aren’t among them. They do recommend that you not fly for 5-times the maximal hour dose interval after taking certain medications, but presumably you are off the pain meds by now.
If your doctor clears you for normal activity (including driving) then you would have no reason to know of any medical condition that would make you unable to meed the requirements of the medical certificate.

14 CFR §61.53   Prohibition on operations during medical deficiency.
(a) Operations that require a medical certificate. Except as provided
  for in paragraph (b) of this section, no person who holds a medical
  certificate issued under part 67 of this chapter may act as pilot in
  command, or in any other capacity as a required pilot flight
  crewmember, while that person:
(1) Knows or has reason to know of any medical condition that would
  make the person unable to meet the requirements for the medical
  certificate necessary for the pilot operation; or
(2) Is taking medication or receiving other treatment for a medical
  condition that results in the person being unable to meet the
  requirements for the medical certificate necessary for the pilot
  operation.

So the FAA says explicitly you're grounded until YOU are cleared by a doctor's notice. They didn't (unless you forgot to mention that) that you need to notify them of such a notice.
So unless the information you provide is incomplete you are cleared to fly again starting February 2020.
To make sure you ticked all the boxes I would at least until your next medical keep that doctor's notice (and get it in writing if you didn't) with your medical and license just in case. Calling that medical hotline and telling them you have said notice may also be a good idea, in case they marked something in your files and they can then mark your recovery. But from what you told us that's probably not required.


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What is the acceptable position of the brake wear indication for A320?
What is the acceptable position of the brake wear indication (PIN) for an A320 to be safely dispatchable?

Just curious, why wouldn't you ask one of the folks that actually work on your plane?

Its always better to know different points of view, that's why StackExchange is there!!

But surely your maintenance department has a policy, that they would be required to follow.  What value then is there in asking for a "different point of view"?

Asking such policies (procedures) to apply them in real-time flights is different than getting to know different points of view just for sharing purposes.

Fair enough then, but these "points of view" aren't generally opinions.  For example, the 1mm limit in the answer you accepted, does this match your maintenance procedure?  If it comes from the Airbus AMM it ought to match every operator's procedure, correct?  So then do you expect something different?  I am all for sharing our differences of opinion to keep things interesting, but some things are pretty black and white...

As a pilot, I don't need to come/match with my maintenance department procedure, since I have to focus on other policies/producers about how to fly and not to fix, and surprisingly pilots might not come across AMM tasks at all, But it wouldn't harm if I knew how engineers do their tasks. I find that interesting to know.

To answer your question the limit is 1mm. It cant be less than this value. At lengths greater than this value brake wear can be measured without any specific brake temperature value. However at values less than 1mm Airbus has a specific brake temperature of 60 degrees Celsius to measure the brake wear.
At high brake temperatures the heat from the carbon brakes causes the pressure plate to expand to which the wear pins are connected to. This can easily cause a false indication of the brakes actual lining wear and if the parking brake is not applied can cause a large false indication. Therefore the recommendation of the cold temperatures. Applying the parking brake is of importance as the actual wear of the brakes lining can be gauged.
As mentioned soo long as it's over 1mm with the parking brake ON it's possible to measure brake wear at any brake temperature.
The official reference as per the AMM is also attached.

@IslamElsayed for certain reasons I can't share that information on open comments.

I can explain the reasons to you via other mediums. Can I contact you on some other platform ?

Unfortunately I'm not on twitter any other platform?

There are two wear pins. If the end of either pin touches the machined part of the piston housing the heat pack is worn out and the brake must be replaced. Measurement must be done when the brakes are cold. If one wear pin is missing, check to make sure the other pin is there and looks ok. If both pins are missing the brakes need to be replaced.


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What is ILS CLASS in this airport NOTAM?
I have seen this NOTAM for UAII /CIT SHYMKENT airport and they mention ILS CLASS for runway 10/28, Does anyone knows what it means?
NOTAM:

NOTAM K3998/20: Shymkent Airport (UAII)
K3998/20 NOTAMN
Q) UAII/QICXX/I /NBO/A /000/999/4222N06929E005
A) UAII B) 2008171542 C) PERM
E) RWY 10/28 ILS CLASS:
ILS GP  I/C/2
ILS LOC I/D/2
REF AIP UAII AD 2.19
CREATED: 17 Aug 2020 15:42:00
SOURCE: EUECYIYN

This is a change in the ILS Facility Classification code. In your example the code is I/C/2 for ILS with GP, which means:

The ILS category is CAT I
Quality of Course C, which means localizer performance follows performance requirements until 100ft
Integrity level 2 (see ICAO Annex 10, Volume I for details)

The changes can also be found in the Kazakhstan eAIP UAII AD 2.19.
Here is a detailed description of the three codes in the classification by ICAO:

ILS FACILITY CLASSIFICATION AND DOWNGRADING
The  ILS  facility  classification  system  provides  a  more  comprehensive  method  of  describing  ILS  performance  than  the  simple  CAT  I/II/III  classification.  An  example  of  an  ILS  facility  classification  is  “III/E/4”.  ILS  facility  classification  is  described in Annex 10, Volume 1. A facility’s “class” of performance is defined by using three characters as follows:
a)    The first group of characters (I or II or III) indicates conformance to the facility performance category standards contained in Annex 10, Volume I. This character indicates if the ground equipment meets a facility performance Category I, II or III.
b)    The  second  group  of  a  single  character  defines  the  ILS  point  (Figure  C-1)  to  which  the  localizer  conforms  to  the  facility  performance  Category  II/III  course  structure  tolerances.  These  classifications  indicate ILS conformance to a physical location on the approach or runway as follows:

A:    7.5 km (4 NM) before the threshold;
B:    1 050 m (3 500 ft) before the threshold (CAT I decision point);
C:    Glide path altitude of 100 ft HATh (CAT II decision point);
T:    Threshold;
D:    900 m (3 000 ft) beyond the threshold (facility performance category III requirement only);
E:    600 m (2 000 ft) before the runway end (facility performance category III requirement only).

c)     The  third  group  of  a  single  character  indicates  the  level  of  integrity  and  continuity  of  service.  It  is  generally  accepted,  irrespective  of  the  operational  objective,  that  the  average  rate  of  a  fatal  accident  during landing due to failures or shortcomings in the whole system, comprising the ground equipment, the  aircraft  and  the  pilot,  should  not  exceed  $1 \times 10^{–7}$.  This  criterion  is  frequently  referred  to  as  the  global risk factor. In Category III operations, this objective should be inherent in the whole system. In this  context  it  is  of  the  utmost  importance  to  endeavour  to  achieve  the  highest  level  of  integrity  and  continuity  of  service  of  the  ground  equipment.  Integrity  is  needed  to  ensure  that  an  aircraft  on  approach  will  have  a  low  probability  of  receiving  false  guidance;  continuity  of  service  is  needed  to  ensure that an aircraft in the final stages of approach will have a low probability of being deprived of a guidance  signal.  Integrity  and  continuity  of  service  requirements  are  defined  in  Annex  10,  Volume  I,  Chapter 3, 3.1.3.12, for the localizer and Chapter 3, 3.1.5.8, for the glide path.

(ICAO Manual of All-Weather Operations)


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What does "ACFT MAX 65/7 " means on lido charts?
What does "ACFT MAX 65/7" on the minima box means? I found out that its related to wingspan and some vertical distance, but I still didn't get the vertical distance thing !!

https://www.pprune.org/questions/554129-lido-65-7-minima.html states that the 7 relates to less than 7m vertical distance required between the paths that wheels and glide slope antenna follow on the approach. It also offers the notion that these minima can only ever be used by A380 at the moment.

so the 7 m vertical distance is when the a/c on the ground or during landing ?! , i still can't imagine he picture in my head .

It’s during approach. The aircraft will travel on a slope pointing 3° downwards, so all its parts will do, too. The aircraft will travel on that path with a certain, in the context of this exercise predefined, body angle (often with the nose pointing slightly upwards). This will lead to the GS antenna (probably in the nose) following a different path than the main gear (but obviously parallel and pointing downward at 3°). Trace these paths, draw a vertical line intersecting both, measure the distance between the paths on this line. Still posting as comment due unconfirmed reference.


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Why is it called "STBY RUD" on a Boeing 737?
(Source: b737.org.uk)
Anyone knows why "STBY RUD" is named "STBY RUD" when the selection of the switch position activates the standby hydraulic system as well as the standby rudder system (by opening  rudder shutoff valve)? Is it because the standby rudder is more important than the standby hydraulic system as a standby system?

According to the Boeing 737 Flight Crew Operation Manual, the "Standby Hydraulic System" only powers the following:

thrust reversers
rudder
leading edge flaps and slats (extend only)
standby yaw damper

It does not power, for example, brakes, ailerons, spoilers and the landing gear.
I speculate that the word is chosen to remind pilots that the system powers the rudder but not other primary flight controls.

Standby Rudder is a separate indicator light that was installed as part of the Rudder Enhancement Program, which was put in place after findings of the NTSB regarding the cause of accidents that occurred in the 90s.

Standby Rudder pressurises the Standby hydraulic system which will power the separate Standby rudder PCU. Above and below pictures are from this site; picture below shows the upgraded system, with one PCU powered by hydraulic system A, one PCU by system B, and a separate Standby PCU powered by the Standby hydraulic system.

From this site:

The 737NG also has a standby rudder PCU that moves the rudder during manual reversion operation. The wheel-to-rudder interconnect system (WTRIS) will coordinate (assist) turns by using the standby rudder PCU to apply rudder as necessary based upon the Captains control wheel roll inputs. From experience, I can verify that this makes the NG much easier to handle in manual reversion than previous generations.

Sorta. "Stby Rudder" was always a position on the Flight Control switch; the RSEP added a new way that the standby hydraulic pump could come on & pressurize the standby rudder PCU -- if the system detected the A PCU and the B PCU opposing each other. In that case, the Stby PCU becomes active (using the Stby hydraulic system) to "break the tie" in favor of whatever the flight controls were commanding. To tell the pilots that this was happening, the RSEP added the "Stby Rudder" light. If it's on & you didn't put a Fit Control switch to Stay Rudder, then the cause is the other PCU's fighting.

There is only one rudder on the aircraft, so speaking of "the standby rudder" would be incorrect -- to describe it that way suggests the presence of a "main" rudder and a second "standby" rudder, and that's not what's on the 737. What you do have is the standby hydraulic system, which is used to provide backup hydraulic power to a few components (listed in @Kevin's answer) when one of the main hydraulic systems (A or B) becomes inoperative.
So the better way to think of "Stby Rudder" would be "Standby Hydraulic System powering the rudder" -- and on the switch, "in lieu of Hydraulic System A" or "... B".  Those switches are used either when a hydraulic system has failed, or to test the standby hydraulic system.  The three positions of each switch are "__ ON" -- so the respective (A or B) hydraulic system is powering all flight controls, "OFF" -- so the respective hydraulic system is not powering any flight controls, and "STBY RUDDER" so that in addition to the "Off" functionality, the standby hydraulic system is activated & powering the rudder.  (Why just the rudder? The ailerons & elevator can be adequately controlled in Manual Reversion -- zero hydraulics -- mode, but the rudder cannot. It has to have hydraulic power to provide the deflection required in case of an engine failure.)
The standby pump comes on automatically under various conditions, essentially all related to loss of a main hydraulic system. So if a main system were to fail on short final, let's say, you'll have the Standby pump running to power the Thrust Reverser on the side where the failed system would normally power it -- no need for an immediate reaction to put the flight controls to Standby Rudder during a critical phase of flight.  In that scenario, your good hydraulic system continues to power all flight controls just fine.
As @Koyovis describes, the RSEP modification added some additional safety features and the "Stby Rudder" indicator light. That light is new with the RSEP mod; the switch position had always been labeled like this.  Essentially, the RSEP mod added sensors to detect if the A-system and B-system rudder PCU's were opposing each other. This is driven by the theory that a rudder PCU can "run away" and cause uncommanded actuation of the rudder to a hard-over position. Were this to occur, the RSEP mod enables the Standby Rudder PCU (i.e. the PCU for the rudder that is powered by the Standby Hydraulic System) to become active & "break the tie" so that whichever PCU is responding to flight control inputs "wins" and overpowers the runaway PCU.  The Stby Rudder On light will come on if the Standby Rudder PCU is powered, and if the flight crew didn't command this by putting either Flight Control switch to "STBY RUDDER" then they know it is happening because of a "force fight" between the A and the B PCU's and that the Standby PCU is working to keep things under control. I've not heard of that happening during actual operations; maybe Boeing has.

Your description is that there is a third rudder PCU. You say that in addition to the "Off" functionality, the standby hydraulic system is activated & powering the rudder. But it is powering the rudder through a seperate standby-only PCU? That would explain the switch marking. The top position turns on, not only the stby hydraulics, but also the stby PCU. Thus the markings of both STB for the hyd system and RUD for the extra PCU. Am I understanding this correctly?

@TomMcW Yes, there is (has always been) a third PCU. Essentially, an A system PCU, a B system PCU, and a standby system PCU. Until the RSEP, at most 2 of these could be simultaneously powered. The standby PCU is near the bottom of the right graphic Koyovis posted.

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text:
Can you fly direct to your destination if you can cruise above FL450 regardless of airways?
To my knowledge, the high altitude enroute charts only apply to the altitudes between FL180 and FL450. Does that mean you can plan direct to your destination if your cruising altitudes stay above FL450?

I'm not sure (if I was I would be posting an answer :P) but I think you have to specify jurisdiction. I guess it has to do with airspace classification, and there are differences between the countries.

@Stelios Adamantidis Actually I meant international flights under ICAO rules, but if it's impossible to talk about it since different countries have different flight rules, I'd like to know at least about the FAA rules on this

This depends on the specific country you are flying over. Some countries make use of free route airspace and similar concepts, others do not

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text:
What are the lateral sensitivities of GPS approaches?
What are the lateral sensitivities of each of the WAAS and LNAV approach? Is the lateral sensitivity of WAAS the same as that of the localizer, which is 3 to 6 degrees? What about the LNAV approach?

What do you mean by sensitivity?

@DeltaLima Like when a full deflection of the localizer CDI means you're three degrees off of the center course to the left or right, what degrees or what distance does the full deflection of the CDI on the WAAS and LNAV approach indicate?

You ask for the "sensitivities" of the approaches, but from your comment it sounds like you are talking about the sensitivities of the instruments. Is that correct? "deflection of the CDI on the WAAS and LNAV approach" doesn't really make sense

Check out AIM 1-1-9 for localizer information. Basically, the localizer is positioned so to have a course width of 700' at the threshold. So full deflection to either side is 350'. A CDI has 5 dots on each side, so at the threshold each dot is 70'. Near the Middle Marker, one dot means you’re off course by 150 ft. Near the Outer Marker, a one-dot deviation puts you about 500 ft. from the centerline.
GPS (non-WAAS) approaches have a constant full scale deflection of .3 NM after the final approach fix.

AIM 1−1−17 5 (e) (5) When within 2 NM of the Final Approach Waypoint (FAWP) with the
  approach mode armed, the approach mode will switch to active, which
  results in RAIM and CDI changing to approach sensitivity. Beginning 2
  NM prior to the FAWP, the full scale CDI sensitivity will smoothly
  change from ±1 NM to ±0.3 NM at the FAWP. As sensitivity changes from
  ±1 NM to ±0.3 NM approaching the FAWP,…

WAAS on the other hand is similar to the localizer.

AIM 1-1-18 (d) 4 Both lateral and vertical scaling for the LNAV/VNAV and LPV approach procedures are different than the linear scaling of basic
  GPS. When the complete published procedure is flown, ±1 NM linear
  scaling is provided until two (2) NM prior to the FAF, where the
  sensitivity increases to be similar to the angular scaling of an ILS.
  There are two differ- ences in the WAAS scaling and ILS: 1) on long
  final approach segments, the initial scaling will be ±0.3 NM to
  achieve equivalent performance to GPS (and better than ILS, which is
  less sensitive far from the runway); 2) close to the runway threshold,
  the scaling changes to linear instead of continuing to become more
  sensitive. The width of the final approach course is tailored so that
  the total width is usually 700 feet at the runway threshold. Since the
  origin point of the lateral splay for the angular portion of the final
  is not fixed due to antenna placement like localizer, the splay angle
  can remain fixed, making a consistent width of final for aircraft
  being vectored onto the final approach course on different length
  runways. When the complete published procedure is not flown, and
  instead the aircraft needs to capture the extended final approach
  course similar to ILS, the vector to final (VTF) mode is used. Under
  VTF, the scaling is linear at ±1 NM until the point where the ILS
  angular splay reaches a width of ±1 NM regardless of the distance from
  the FAWP.


text:
What is the cabin noise hertz in typical commercial aircrafts?
In cabin, we hear noises in commercial aircrafts. Wondering if it is in general over or under 100 hz. There should be a band width. Thanks!

Your question would be a lot better with some context. Why are you asking? The noise is going to be broad spectrum and beyond the range of human hearing in the low frequencies but probably attenuated at high frequencies by the acoustics of the cabin. If you can find a video recording from inside a cabin you can run it through an audio spectrum analyser program to answer your question.

@Transistor I don't think you can use the playback of a video recording to find the answer: The recording device can only record certain frequencies.

Almost everything you hear is way, way over 100 hz.  Are you asking if there are frequencies as low as 100hz in the cabin?

In a jet it's going to be pretty much all above 100hz. Most of the noise at cruise is broad spectrum "white noise" from the air flow and the engine core exhaust.  The fan however, running at, typically 4000 rpm, with 60 blades say, will be producing a 4000 Hz noise, and this along with the exhaust white noise will be the dominant sound prior to cruise.
In a propeller driven aircraft however, you will have noise below 100 hz from the prop.  A 2 blade propeller spinning at 2200 RPM is imparting a 73Hz pressure wave pulse on the windshield and this is one of the dominant forms of noise in that case.  Next is the exhaust pulse from a 4 cyl engine, 2 per revolution, also giving 73 Hz at 2200 RPM.  Then random frequency mechanical noise from the engine and white noise from the airflow.
So in a Cessna 172 at take off, running at 2700 rpm, you're going to have mostly a 90 Hz sound from the prop and the engine, then some random noise from other mechanical noise from the engine plus airstream white noise.
This is a problem for pilots who use foam earplugs only when flying.  Foam plugs only attenuate sound above maybe 5000 Hz and don't help all that much with the prop and engine noise. ANR headsets are a huge help here because ANR systems work best on low frequencies although not so good on high frequencies.
So when I'm flying I use both an ANR headset and ear plugs.
After I tried out a set of  Isolate Earplugs (and promptly lost them, although they do work), I've also developed my own low frequency earplugs by wrapping about 3" of half inch lead tape (used for ballasting golf clubs) around the shaft of a 3M Push-In earplug (the kind with the little yellow bulb on a blue plastic shaft) and covering the tape wrap with heat shrink tubing.  I put them in with a bit of lanolin on the foam bit to lubricate and improve the seal.  They do a fantastic job of attenuating low frequencies below 200 Hz, and make the ANR headset nearly redundant.

Thanks! This is an amazing answer!

Very interesting answer indeed!

@John K  Just did a study of the performance of ANC headsets for non-professionals. It appears that one Bose headset was ok for hz range of over 100 hz, and acceptable for hz range of under 100 hz. One Sony headset was good for hz of over 100 hz but none for hz under 100 hz. If you were offered the two option what would you choose? You mentioned most jets have all over 100 hz so Sony seemed to be the clear winner?

Do you mean just audio headsets to wear as a passenger?

Hi John, for now yes I do. I haven't got a change to obtain the license yet.

A subtle running gag in the 1980 comedy movie Airplane! is that the jetliner's background noise is that of a propellor airplane.


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USB interface for FDR?
Currently I am investigating the feasibility of transmitting a limited amount of FDR data via radio link for domestic flights within continental USA. I am working on building a prototype system in which I need to connect the FDR with a computer. USB interface is the most appealing one. I am using a small Flight data recorder (FDR) which has a USB interface. However, it is for hobby planes. Is there a USB interface for FDR's in the passenger planes? Or something that converts between ARINC and USB?

Not sure where to start on this... there isn’t a USB port on any FDR I know. FDR is not designed to be read from in air. Also, FDR is not the best box to connect to. Most aircraft have something along the lines of an acquisition unit collecting all data and routing it to FDR. Some aircraft provide something similar to what you want from that acquisition unit via ACARS transmission already. In any case, before you patch anything into a commercial airliner, you required a Supplemental Type Certificate from your authority before being allowed to do that.

Thanks Reynolds for the info. I think there is a Data acquisition unit in modern planes (DAU) that pulls the data from black box. In emergencies during landing and take off, DAU can send tons of data to ATC on demand.

Sorry, pressed ENTER too soon. I believe modern FDR is already a computer. All I need to do is add my software to it that would pull the safety data and transfer it to the cloud regularly. In the long run, I think OEM is the way to go if any FDR company is interested in this product.

I don't believe anyone is transmitting all the 88 FAA mandated parameters all the time.

@Junaid you don't seem to understand that you will not be allowed to plug in ANYTHING in flight to the FDR or any other system without certification from the FAA. This isn't a cheap startup project, you need deep pockets to do this. No way around it.

I agree with you Juan. That is why I would look for OEM possibility.

I am looking into smaller niche markets that may not need FAA certification to add any hardware/software such as hobby planes, drones, private planes etc.

Certified FDR's for commercial aircraft don't have USB ports. They have interface ports because you obviously need to be able to extract data, but they are usually proprietary and each one uses a specific cable for the FDR you want to talk to. To do what you want to do you'd have to design a device that talks to FDR units to download and decompress the data. There are commercial test set units out there that can do this. They are not cheap. As was mentioned in a comment, to do this while in flight will require an STC from the FAA. Also, converting between ARINC and USB doesn't make sense. ARINC is a company, USB is a computer interface specification.
That said, I don't think connecting to the FDR is the best way to do this. As was mentioned, ACARS may already do part or all of what you are interested in doing.

Juan, please see my previous comment to Reynolds. I will appreciate any advice. I found one ARINC-to-USB adapter by ASTONICS Ballard Technology but it costs $4,000. Pretty expensive for just an interface.

@Junaid: 4000 is a small amount for any business developing flight data transmission systems for certification for use in commercial passenger transport aircraft. If you can't afford $4000 you are unlikely to have sufficient resources for a project of that significance.

Yes I agree with you. However I just wrote to dispel the impression the previous comment created that there was no way to convert between ARINC and USB.

Like I said in my answer, there is a way, but it is a test set, not certified for use in flight.


text:
What is this airplane with small wings at different angles seen at Paphos Airport?
I landed in Paphos Airport in Cyprus and spotted this thing sitting in the sun near the runway. It has small 'wings' sticking out at different angles. What kind of plane is this? (Sorry for the bad photo.)


text:
Need help identifying planes, near Toronto

Any help will be appreciated. Thanks

Why do you need this?  Idle curiosity?

Could you please split these questions up (one question per plane you want to identify, multiple pictures for the same plane are OK)?

Top one's a Convair 580 and the middle one's a Challenger 300 business jet.

The last one is almost undoubtedly a Pilatus PC-12 operated by Ornge.


text:
Why does the auto brake panel on an A320 use "lo", rather than "low"?
Is there a specific reason that Airbus chose to shorten "LOW" to "LO" for the lowest autobrake setting?

Wouldn't it be more consistent to use three letters for each setting?

Meanwhile, on Boeings, it says "Low...Med...Neo..." :)


text:
Does a RC aircraft require suspension in landing gears?
we engineering students are preparing for a particular competition with dimensions of 170 in. (length + breadth + width) for that competition we require landing gear but for that are we supposed to use suspension in it?

Probably depends on how heavy it is.  What is breadth? Circumference of the fuselage?

For one that size, you'll certainly need some spring in the landing gear, but it's likely that shock absorbers are still unneeded.  Most models use spring wire landing gear legs, at least up to around 5 kg weight.  As big as your model will be, you may need hinged gear legs with spring return, or something similar.
I'd suggest looking at the landing gear for smaller crewed aircraft (like a Cessna 152 or Piper Tomahawk).  The smaller Cessnas for certain have only spring legs for the main gear, though they use a shock strut for the nose.  Scale down from their practice and you should be good (though scaling down frequently means simplifying, as well as making smaller).

Thanks a lot for your answer. It's really helpful


text:
Can the touchdown RVR be replaced by the midpoint or rollout RVR?
When there are three RVRs equipments in place and an ILS approach chart minumum for the runway simply says "RVR 800m" without any additional notes, is the touchdown RVR the only controlling RVR? If so, what if the touchdown RVR is out of order? Can the touchdown RVR be replaced by either the midpoint or rollout RVR?


text:
How do pilots of big jets determine if they are clear of the runway after landing?
The pilots of small aircraft can easily determine if they're clear of the runway by visually looking back through the side windows.
How do the pilots of big commercial jets determine that all parts of their aircraft are clear of the runway after landing? It looks like the same visual check as used by GA is almost impossible given the size of their aircraft. Do they have some special ways or measures to do that?

After takeoff or landing?

@Ben I meant after landing.

Using TLAR (That Looks About Right).  Pilot turns off a runway onto a taxiway spur and sees the runway safety area lines and just estimates a point beyond roughly equal to or greater than the length of the fuselage and places the cockpit over that point.
Other methods include geo-referenced airport diagrams on a moving map display showing the position of the aircraft.

Your answer begs me a question. Is it safe to use TLAR? What if their guess is wrong and the tail of the aircraft stays well outside the hold short line? I'm curious whether there was any accident caused by this.

@lemonincider If they're still on the runway then the next flight will see that, and go around/not takeoff. Remember, all pilots have eyes, not just the ones vacating the runway.

@J. Hougaard You misunderstood me. That's not the situation I was talking about.

Yes it's fine.  A lot of flying is estimation and being conservatively over.  If he's no clear of the active the tower will growl at him to move.  I've never heard of cases where pilots miscalculated clearing a runway on a taxiway.

Wouldn't the tower generally be keeping an eye on runway clearance and directing loiterers to continue, also?

@lemonincider My experience was in 747-100/200 in the 1990s, and back then at least TLAR worked fine. Pilots internalize (for lack of a better word) the size of the airplane they fly constantly, and they just know where the wingtips and the tail are going to be. I never heard of anyone leaving their tail out on the runway. A captain might have to remind a fresh first officer not yet accustomed to the airplane of something pertaining to the size of the aircraft, but people catch on quickly.

@StarWeaver https://www.youtube.com/watch?v=xjeyQdvxgj4 "his speed was mini"

Weren't cameras introduced on the A340 for this reason? Too hard to tell where such a long airplane actually is without some help.

An inexperienced pilot might underestimate his length by ten or twenty feet, say. But they probably also leave a safety margin. Also there is a safety margin in that the 'runway zone' is wider than a landing aircraft actually needs. Aircraft also very rarely stop as soon as they report clear, and there tends to be a long gap between reporting clear and the next landing aircraft actually passing the point of exit. All of which adds up to this not being a problem.


text:
When leaving ground effect, why is there a nose-up change in moment?
The Airplane Flight Handbook states:

The aircraft leaving ground effect will

Require an increase in AOA to maintain the same CL
Experience an increase in induced drag and thrust required
Experience a decrease in stability and a nose-up change in moment
Experience a reduction in static source pressure and increase in indicated airspeed

I'm having a hard time understanding the number 3 here.
What's the aerodynamic reason for the nose-up change in moment after leaving the ground effect?
Is it because the downwash from the wings increases as the aircraft leaves the ground effect, thus placing a greater downward pressure on the horizontal stabilizer?

Commenting because this is just a guess, but I'd think that in ground effect the extra lift comes from high pressure air with a relatively even p distribution on the lower surface, but once you leave it and go into normal flight lift is mainly from the low pressure on the upper surface, which is concentrated near the leading edge. Therefore as you leave ground effect the combined centre of pressure on the wing moves forward, creating a pitch-up moment.

Very interesting idea. I'd like to hear what others think about your guess.

@Talisker Once you leave ground effect, the wingtip vortices start to produce induced drag and slight negative lift at the wingtips, adding to the pitch-up moment.

@JScarry-- wouldn't negative lift at the wingtips only contribute to a pitch-up moment in a swept wing aircraft?

The aerodynamic centre of a wing shifts when it is in ground effect. Out of ground effect, the wing produces lift by accelerating air downwards. In ground effect the ground prevents the air from being deflected downwards, and more lift is produced due to increased pressure underneath the wing. This pressure has a different distribution than out-of-ground effect pressure, hence the change in pitching moment.
Consider a cross section of a wing: free stream lifting force centre is at the quarter chord point. If the wing was supported by just static pressure only, like a hovercraft, the force centre point would be at 50% chord.

Actually not sure now if the horizontal tail has much influence but
  I'll leave the original answer underneath:

Ground effect works by increasing static pressure underneath the wing and the horizontal tail. The aircraft flies out of ground effect in a nose-up attitude, and depending on tail configuration it can be possible for the main wing to be out of ground effect while the horizontal tail still experiences increased pressure underneath, therefore creating a nose-down pitching moment. Once the horizontal tail flies out of ground effect as well, the nose-down pitching moment disappears. I would not expect that T-tails have this change in pitching moment but I have never flown one.

I am not sure that I follow you on the increased pressure underneath causing a nose down pitching moment. Normally the increased pressure underneath is at the wing.  The tail usually provides a slight downward force.  A canard would be a good example of an exception. The game changes a little for lifting bodies and some other not so conventional concepts.

Yes conventional horizontal tail exerts a downward force. If there is more static pressure underneath it it exerts less of a downward force -> more nose up moment. However it turns out that the aerodynamic centre shifts when the wing itself is in ground effect, I've updated my answer.

Less downward force on the rear end of the plane would be less of a nose-up moment, I think.

Koyovis' explanation is correct and deserves to be the accepted answer. However, as always, much depends on the details of the specific configuration - generalizations like those in your question deserve to be treated with some caution.
Ground effect does not always result in a pitch-down change. The Handley-Page Victor was famous for its ability to flare all by itself when entering ground effect. From Wikipedia:

One unusual flight characteristic of the early Victor was its
self-landing capability; once lined up with the runway, the aircraft
would naturally flare as the wing entered into ground effect while the
tail continued to sink, giving a cushioned landing without any command
or intervention by the pilot.

The key factors were the T-tail and the low crescent wing: Since the wing would enter ground effect much earlier than the tail surface, its lift  would increase earlier. The low wing in combination with the high tail would add a pitch-up change in ground effect.
Why is the lift curve slope different in ground effect? The proximity of the ground reduces not only the downwash angle but also the induced angle ahead of the wing. A highly cambered wing with low angle of attack will experience a reduction in lift. However, with a positive angle of attack the airflow below the wing will be partially blocked by the ground, so pressure will increase below the wing and force more air to flow around the leading edge and over the wing, resulting in an increase of the lift curve slope.
With a low tail, the handbook is correct, however: Since the tail flies in the downwash of the wing, a reduced downwash results in a positive angle of attack change at the tail, increasing lift there and resulting in a pitch-down change. This comes on top of the change in the pressure distribution over the wing which shifts the center of pressure backwards, adding more nose-down pitch, as described by Koyovis. Leaving ground effect will lower the angle of attack at the tail and makes itself felt as a pitch-up change.
The F/A-18 has suffered from this effect and needed a kludge to restore its pitch control power to the out-of-ground-effect value, namely toed-in rudders. As Jan Roskam explains in his book "Roskam's Airplane War Stories" (War story 108):

When the first F-18 fighter […] was flight tested at Patuxent River,
it became evident that the airplane would not rotate at the predicted
speed. This made the field performance of the airplane unacceptable.
The problem was traced to an error in the calculation of aerodynamic
forces in ground effect. This is particularly severe in case of a low
placed horizontal stabilizer. As a result there was insufficient
down-load capability to effect early rotation during the takeoff
ground roll.
The problem was fixed by toe-in of the rudders. A squat-switch on the
main gear biasses the rudders to deflect inward while on the ground.
This creates enough positive pressure over the aft fuselage to effect
early rotation.
This fix, although impressive, came at a price. All flight control
software had to be revalidated. Also, the squat-switches represented
additional system complexity.

As you may already know, when an aircraft is in ground effect the upwash, downwash and wing tip vortices are all reduced which means the wing behaves as though it's aspect ratio has been increased that is to say the induced drag and angle of attack are reduced for the coefficient of lift.
An aircraft can become destabilised climbing out of ground effect because if a constant angle of attack is maintained it may experience a loss of lift which in turn would further increase the nose up movement.
In conditions such as high temperature and a high all up weight it could prove impossible to climb out of ground effect.

I had the same idea at first but I concluded that idea is covered by the number 1. The number 3 is not referring to a deliberate pitch up movement by the pilot, which as you mentioned is required to make up a loss of lift experienced leaving the ground effect. The pitch up movement here is a spontaneous movement as the aircraft leaves the ground effect, thus requiring the pilot to push the yoke a little bit if he wants to maintain the pitch angle. Please correct me if I'm mistaken.

The pitch up movement is indeed as the aircraft leaves ground effect which is normally counterbalanced by trimming the aircraft down a notch or two to climb. It's also logic that the aircraft becomes more stable as it begins to accelerate.


text:
Why is the use of reverse thrust not considered when calculating accelerate-stop distance on dry runway?
In calculating the accelerate-stop distances, what are the possible reasons why the use of reverse thrust is not taken into account on a dry runway, while it is taken into account on a wet runway? What's the rationale behind this diffentiation, when at least as I see it there's nothing that prevents the use of reverse thrust on a dry runway for an aborted takeoff?

SOP's may require the use of reverse thrust on wet/contaminated runways while not on dry runways.

Seems to be risk management. Reversers are relatively, for an aviation technology, unreliable, so you don't want to rely on them too much.

If your thrust reversers are operational and debris is not a concern, you're right for an in-service rejected takeoff (RTO):

There's nothing that prevents the use of reverse thrust on a dry
  runway for an aborted takeoff.

Most in-service RTOs utilize reverse thrust if available (see this video for a dry-runway example).
However, in order to certify a transport-category airplane, one must show compliance with 14 CFR 25.109, paragraph (f), which precludes the use of thrust reversers on dry runways in calculating the accelerate-stop distance. The demonstration required by paragraph (i), therefore, cannot be conducted with reverse thrust on a dry runway. From a certification standpoint, the accelerate-stop calculation is made the way it is because that's what the regulations say. But why is the law written this way? See this video at about 1:12:

The whole intent is to demonstrate [that] under [the] worst conditions you can safely stop the aircraft.

"Worst conditions" encompasses at least inoperative thrust reversers and worn brakes.


text:
Does TSR (Time Since Repair) Need A Reset After A Clean/Inspect/Test Workscope?
So I am a little unclear on what the regulations recommend.
Say you have a component that has a Restoration (Ignore the nomenclature) workscope but it is strictly an Inspection/Cleaning/Testing process. The FAA/EASA tags would say Inspected/Tested.
Does that mean the TSR/CSR (Time Since Repair / Cycles Since Repair) need to be reset to zero? Or would the TSR/CSR continue as-is because there was no Repair work carried out? Any assistance would be appreciated.

If there is a Restoration task in the Maintenance Program, the time will be tracked based on the hours/cycles the Restoration was performed.  How does "repair" come into it?  If it goes in for a repair "out of phase" it can be considered compliant with the restoration interval and zero timed from that standpoint, but may require language in the repair documentation that says the repair meets the restoration requirement.  Restorations like that that don't involve parts replacement are usually due to a grease/lubricant replacement requirement.

@JohnK Thanks for your reply. I have observed various EASA/FAA tags mentioning TSN/CSN, TSR/CSR and TSO/CSO. Generally the maintenance organistions will change the TSR/CSR to zero after a Repair work but for Test/Inspect as well some of them reset TSR/CSR to zero but some continue the TSR/CSR as per last known values. What do best practices recommend?

Is this under an MSG-3 based maintenance program or something else?

Yes, this is MSG-3 indeed

In an MSG-3 based maintenance program there's no such thing as "overhauled" as in "put back in new condition and reset to zero".  Line Replaceable Units will be qualified operationally and structurally under an endurance/fatigue test program and will normally have a structural life limit where a unit carries structural loads of some kind.  If there is no applied life limit the part can be theoretically run forever (or at least the certified life of the airframe), because under MSG-3, components can be run indefinitely until some form of inspection or test in the field detects a degradation beyond a limit.  Think functional test, leak test, NDT, visual inspection etc.
What happens with LRUs is they may fail or some internal parts may fail during endurance testing. The part was designed to run 80000 cycles, was tested to 120000 cycles (1.5 scatter factor margin for mechanical parts), and say a bearing and thrust washer failed during the testing at 60000 cycles of testing. Those parts will be replaced and the endurance test continued to the end.
But now when it's certified, there will be a need to send the unit in at 40000 cycles (1.5 scatter factor applied to 60k) to "restore" it to its pre-test failure condition.  The unit has to go in, be disassembled and reassembled and any parts that are out of serviceable specs replaced, but the parts mentioned in the restoration task must be replaced, serviceable or not.
Sometimes, a part with a grease charged gearbox will have a restoration applied because the grease was found to be breaking down during endurance testing, and the grease is the only component that must be replaced.  The restoration task in the maintenance program will say specifically what has to be done, as in "replacement of the grease" or "replacement of the Main Ballscrew Thrust Bearing and Washers, PNxxxx and xxxx" (Operators get mighty mad when they send some part in for replacement of grease or 40 dollars worth of needle bearings because the Maintenance Program requires it, expecting a 2000 dollar bill, and the unit comes back with half the guts replaced and a 15000 dollar repair bill because other parts were damaged or worn out prematurely).
When an LRU goes in for repair not related to the maintenance program (like a random breakdown), whatever parts are replaced will be those that are out of service limits or are considered needed for the unit to pass an outgoing Acceptance Test Procedure (functional test in a test rig).  When it comes in for repair, it will get an incoming Acceptance Test done (the same rig test), and if it passes, it may go right back out No Fault Found unless the operator specifically demands it be torn down anyway. In any case, a repaired part does not come with any reset to a Life Limit, but it MAY reset the restoration interval if the restoration requirements were met during the repair.
The Life Limit applies to the root housing (the structural part with the serial number) and when a unit gets to the life limit in total hours/cycles it is scrap even if it was fully "rebuilt" 5000 cycles ago when it was sent in for a repair (so you generally try to avoid doing that).
Anyway, under this type of maintenance program, what needs to be tracked are total hours/cycles since manufacture to which the LRU's Life Limit applies, and hours/cycles since Restoration, (and hours/cycles since functional test, or some inspection obviously) where the maintenance program has a Restoration task applicable to an LRU (like a screw jack that has to go in every 30000 cycles to get a set of bearings changed).
So.. if you had a part with a tag that has "time since repair" on it, that information is not sufficient, and has no real effect on anything, because the only mandatory removal interval under MSG-3 is the Restoration task and the Life Limit.  If a screwjack's tag says it was repaired at 20000 cycles, and there is a 30000 cycle Restoration in the maintenance program, you're going to have to send it back in in 10000 cycles (when it gets to 30k) unless there is language in the shop paperwork that states that parts mentioned in the  Restoration were replaced, or there is a statement something to that effect.  If that's the case, you can now run it to 50k, the next 30k interval.
Then when it gets to the life limit, it is trash even if it just went in and had a complete and total "overhaul" done where everything but the gearbox was replaced, following a random breakdown in the field. An LRU that breaks down a few thousand cycles short of its life limit will normally go in the trash.

Did the LRU require Repair or Overhaul?  If not, then no reset. Your description of clean, inspect, and test would be applicable to "Inspected/Tested" status.
Use the status block on FormONE or 8130-3 to guide reset of TSO/CSO or TSR/CSR.
Typical regulatory guidance on this block is use the status which represented the majority of the work performed this shop visit: e.g. Modified, Inspected/Tested, Repaired, or Overhauled.
Note: TSN/CSN should never be reset.
Airlines track "soft" times on LRU's to optimize scheduling times between shop visits to minimize unplanned removals during Aircraft Operations which cause flight delays and interruptions to their schedule.
Only Life-Limited-Parts (LLP's) have "hard" limits. These are the fatigue parts previously mentioned by John K.  LLP's are subject to strict regulatory rules for technical record keeping and mutilation at disposal.


text:
Why are birds attracted to airports?
Birds are usually around airside. Apart from answering it myself, I am looking for community knowledge on this topic.

They probably enjoy watching the planes

Same principle as hunters using giant decoy geese

ARE birds actually attracted to airports?  Compared to say other open grassy spaces like parks...

Welcome to aviation.SE! If you don't get a good answer here you might try asking on biology.SE. As jamesqf pointed out, it isn't clear if birds are more attracted to airports than to any other similar environment. The reasons why birds prefer one place to another seem more like biology than aviation to me.

Airports are a wide, open space with a full environment. The attractiveness of vegetation is a balance between food presence, food accessibility, and protection against predators.

And these factors vary a lot for every bird or animal species.
Food
Food accessibility depends on vegetation height and density. Long, dense vegetation will inhibit most hazardous birds/wildlife from moving around, detecting and accessing the food. In addition, birds/wildlife feeding on seeds will avoid the airport if its vegetation is mowed during the flowering season.
Depredators
On the other hand, many species prefer to stay in the open space of short vegetation where they have a wide view to see predators well in advance to enable them to flee on time; and safeguard themselves from predators by hiding or fleeing.
(from AirportBirdControl Blog: 6 most asked questions and answers)

Just to be clear, I am the author of the post.

Please make sure to cite the sources for your images by editing them into your answer.


text:
How does ADS-C and FMS relate to FANS?
So - I'm totally confused about FANS and its systems. From what I understand:

FANS 1/A (started in 90s) has some early CPDLC for USA routes (this topic) but what about position reporting? Does it have ADS-C (or other ADS system)? And if it does not, what is used for position reporting to the ATC? Also - is satcom used in the FANS 1/A as a message-transporting service or not? And what is the role of FMS in this system?
FANS 2/B has LINK2000+ CPDLC and ADS-C and uses onboard ATSU to transfer its messages to the ATC. ATSU automatically selects the best form of communication (VHF, Sat, HF...) to transfer the messages. What is the role of FMS in this system? It provides info for ADS-C and provides data to CPDLS or am I wrong?

Thank you. There are so many sources and they differ from each other and I really need to be clear in this.

Rampant use of acronyms without first spelling out what they are is not conducive to getting answers to your question.

This is not APU or VOR. These very specialized acronyms. I will simply ignore questions that do this.

@JuanJimenez Well - one would say, that API and VOR are very specialized acronyms as well. Not that off from FANS and CPDLC. Plus I doubt that if you are not able to tell what these acronyms are, you are not the best guy to answer the question, so you can simply ignore it, as you've stated.

I mean APU ofc (cannot edit again), tho API (advanced passenger info) exists in aviation as well :-)


text:
Can Python be used onboard systems on aircraft or military jets?
Was working on a python related to avionics, came across a serious doubt whether code written in python would compile or run on a real time OS used in on board systems.

From a software certification viewpoint, you are going to have a much more difficult time certifying Python software in a safety critical application. Even C++ can require more work than C or Ada. The related question @ymb1 shared has some very useful information.

See https://stackoverflow.com/questions/7079864/real-time-operating-via-python/24819846

It also does not help that Python cannot be compiled to machine code. Many people talk about Python compilers but they are all interpreters. Use the right tool for the job.

You can compile Python as an executable @JuanJimenez, but that defeats the purpose IMO. Python is great but I wouldn't stake my life on it! Give me Ada.

@GdD If you are talking about PyInstaller, that is not a compiler, it's a resource bundler. The result is still interpreted, just easier to distribute. Same with py2exe.

A non-trivial RTOS can run lower-priority tasks that don't have to be real time; certainly there are ways to run python or at least microphython in such a setting if there's a sound reason to.  Modern aircraft have dozens if not hundreds of distinct systems segregated for distinct purposes (likely including level of auditing necessary), not all of them remotely real time.

Good point @JuanJimenez.

The other point to consider is that not everything on an aircraft runs on an RTOS. Some entertainment systems even run WindowsCE. Of course, no one appeared to have considered the effect of a BSOD on the average garden variety houseplant-level passenger. :)

Many military jets (and other systems) still rely on ADA for a programming language, and for good reason. ADA, despite being very old, is an extremely powerful language and has built-in protections.

You need a real time program. Python (current implementation) cannot offer such guarantee. You may need to check old discussion about Linux Kernel for real time: hits: doesn't depend on speed, in fact real time is often slower, but guaranteed.

Language like Python, Java or C# require complex execution environment to run. This environment consists of tens and hundreds of thousands lines of code. It would be a huge work to review and certify it all, so certifying a Python application is not about reviewing ten lines of code that implement the needed algorithm.
While there are also various libraries for C or C++ as well, they are all optional. There is much more built-in stuff in high level languages, starting from the memory garbage collector that alone may be enough to make the implementation too complex to deal with.
Also, high level languages tend to have slightly unpredictable execution speed with short arbitrary pauses (they are not real time). This also limits where they could be used.


text:
What is the power curve
Someone help me understand this thing in a simple way.
I understand it helps determine Vx.

Can you tell us what you mean by the power curve? Without any context, it's very difficult to know what you're asking.

The website How it flies? have a specific section about power curve. You may read this section as it brings complementary information to current answers.

It's an expression of power required to maintain level flight throughout the speed range of the airplane and forms a U shape.  The lowest point of the curve, bottom of the U, is the point of minimum power required for level flight and is normally just below maximum L/D speed (flattest glide speed).  To go faster moves up the U to the right and requires more power.  To go slower moves up the U to the left and also requires more power.
The main bogey man that pilots have to be aware of is the issue of being on the "back side". If you slow to below min power airspeed, slowing any more will require more power to keep from descending; that's the back side.
This becomes a crisis situation in marginal conditions, especially when flying at very high altitudes, and is one of the things that makes flight at the upper flight levels riskier than at lower altitudes; if you are flying at Min Drag  speed or close to it at service ceiling, say FL410, and fly though some down flowing mountain wave air that is sinking at 100 fpm (nice smooth air that you likely won't notice), the autopilot in ALT hold mode will just pitch you up to keep from descending and the jet will slow down.
If you aren't paying attention and let the speed bleed off too much, you will find yourself in a pickle entering the back side of the power curve, with little reserve thrust to speak of, and will have no option but to tell ATC you have to descend NOW and start down until you can recover your speed.


text:
Is Auto Pilot capable of performing TCAS resolution advisory?
I just watched a near mid-air collision video clip on Youtube. When AP is on and TCAS gives resolution advisory ("climb climb" or "descend descend"), does AP automatically perform the advisory if the pilot doesn't take over in time?

I know that there are certified TCAS/autopilot/FD systems (380 comes to mind), but the normal modality that I am familiar with is where TCAS alerts are provided to the pilot, who then decides what action to take.
As for the rules on the certified systems, I cannot comment, but I am sure that information is obtainable.
Of course, one can imagine one avoidance maneuver triggering more avoidance maneuvers, and a cascade of paperwork at ATC. So the rules and use cases are likely heavily vetted.
To generally answer your question, the most common TCAS implementations do not couple with AP or FD, and rely on pilot decision making to further avoid conflict.
Addendum #1
The A380 does apparently have an integrated AP/FD mode that works with TCAS.  I don't know the rules and the certification criteria and goals, but here is an article on it.
http://www.airbus.com/newsroom/press-releases/en/2009/08/easa-certifies-new-autopilot-flight-director-tcas-mode-for-a380.html

I thought I saw a system for TCAS driven AP / FD for the A380.  I may be mistaken.

http://www.airbus.com/newsroom/press-releases/en/2009/08/easa-certifies-new-autopilot-flight-director-tcas-mode-for-a380.html

Short answer is no.
First of all it is resolution advisory as you said. Its purpose, is to make the Pilots aware of an imminent danger/conflict. As with 'Terrain, Terrain', 'Pull up!, Pull up!', it is up to the pilots whether or not they will follow the instruction (normally they always do, but there are exceptions).
However when the pilots hear 'Climb, Climb' or 'Descent, Descent', or another TCAS alert, they should immediately initiate the required action. After all, these days there are top-notch ATC and confliction prevention systems, as well as high-tec TCAS systems on most of the commercial aircraft.

Wrong answer. Some aircraft, for example Airbus 350, have the capability to perform TCAS RA with AP on.

On most aircraft: NO.
On some aircraft: YES.

On most aircraft A/P is incapable of executing the maneuver advised by TCAS RA. The evasive maneuver has to be flown manually. Thus if the A/P is engaged, it has to be disengaged.
Taking the A320 as an example, the A320 TCAS procedure & memory items are (excerpt):

AP (if engaged)……………………………………… OFF
BOTH FDs………………………………………………………… OFF

PM selects FD’s OFF after request of PF.
Respond promptly and smoothly to a RA by adjusting or maintaining the
  pitch, as required, to reach the green area and/or avoid the red area
  of the vertical speed scale.
Avoid excessive maneuvers while aiming to keep the vertical speed just
  outside the red area of the VSI , and within the green area. If
  necessary, use the full speed range between Vαmax and VMAX.
Respect stall, GPWS, or windshear warning.
Notify ATC.

On some aircraft A/P is capable of and will autonomously execute the TCAS RA maneuver:

Some aircraft are equipped with AP/FD TCAS MODE ENGAGEMENT capability.

If an RA is triggered, the AP/FD TCAS mode automatically, and immediately engages.
The PF announces the AP/FD TCAS mode engagement, like any other FMA changes.
If the FDs are disengaged, they automatically engage. The FD pitch bar
  does not flash, and the triple-click aural alert does not sound, in
  order to avoid to disturb the PF during the evasive maneuver.
If the A/THR is disconnected, it automatically becomes armed or active.
If APs and FDs are OFF when the RA is triggered, HDG automatically engages.

TCAS procedure with AP/FD TCAS:

If an RA is triggered:

If the AP is engaged:

The PF should keep it ON.
The AP guides the aircraft in accordance with the RA orders.

If the AP is not engaged:

The PF smoothly and firmly flies the FD pitch bar.
The FD orders guide the aircraft in accordance with the RA orders.
The PF can ask the PM to engage the AP.

The PM monitors the evasive maneuver. He does not try to see the
  reported traffic.

The flight crew checks that the guidance of AP/FD TCAS mode leads the vertical speed out of the red area of the vertical speed scale,
  and in the green area if any.
If for any reason during an RA, the aircraft vertical speed does not reach the green area of the vertical speed scale, the PF should
  disconnect the AP, and override the FD orders, in order to lead the
  aircraft vertical speed out of the red area of the vertical speed
  scale.
If necessary, the PF must use the full speed range between Vαmax and Vmax.
If any “CLIMB” aural alert sounds during the final approach, the flight crew should first apply the AP/FD TCAS procedure. When clear of
  conflict, depending on the situation, they can consider a go-around.
The PM notifies the ATC
When clear of conflict:

The AP/FD TCAS mode automatically reverts to V/S, in order to
  capture the FCU selected altitude. In some cases, the AP/FD TCAS mode
  may revert to an altitude acquire mode or an altitude hold mode.
The PM notifies the ATC
The PF engages an appropriate vertical mode, or adjusts the vertical speed target, in accordance with ATC clearance.

The AP/FD TCAS mode is speed protected, i.e. it ensures that the aircraft speed remains between VLS- 5 kt and Vmax. Therefore, in the
  case the RA is triggered when the aircraft is close to its performance
  limits, the RA vertical speed target may not be reached with the AP/FD
  TCAS mode.


text:
What's field excitation in an electrical system?
"A field relay in the GCU (generator control unit) allows or prevents field excitation within the generator. When open, the field relay deprives the associated power relay of its ground, which causes the power relay to open."
It's an excerpt from the Citation M2's pilot training manual. What's field excitation here?

Better suited to Electronics stack exchange. Short answer: it's an electromagnet. https://en.wikipedia.org/wiki/Field_coil

Excitation on a (usually DC) generator means generating a magnetic field with coils in order to create virtual magnets (inductors). Without current in the inductors, there is no current in the inducted, and nothing is generated. Excitation is used to start the generator, it can be self-excitation (auto created) or an external source. See this.

To my knowledge the M2 uses a Williams FJ-44 engine which has a starter generator on it.  My recollection is that it is a 200A 28VDC starter-generator (SG) which is directly connected to the accessory drive (along with the oil pump).  If 24-28VDC is applied to it, it will start turning the turbine, for starting the engine. At a certain point, once the engine starts, it is switched so that no power goes into it, and instead power is derived from it to charge the battery and provide gen power to the bus.

A typical engine starter configuration is shown above, and is common in smaller turbine engines. Note that the starter generator functions as an electric motor, and also as a power source. (Ignore the circuitry for ignition, throttle relays, etc.)
The SG is NOT an AC generator as is common on transport sized aircraft.  It is also NOT an alternator, as is common to piston engine aircraft.
You may find the descriptions in this manual http://content.aviation-safety-bureau.com/allmembers/faa-h-8083-32-amt-powerplant/sections/chapter-5.php#4. helpful in general understanding of SG operation.  Some of the terms vary from SG vendor to SG vendor, but in general, they are DC motors, and when electric power is removed from them, and they are spinning, they will produce power. Some are self excited with residual magnetism and others utilize an internal circuit to take the small power created by residual magnetism to create a stronger field to create a larger output power from the generator.
Having said all of this, normally a field excitation coil, is the name attributed to an alternator field, which is a magnetic field created by current (not residual magnetism, and not a permanent magnet).  An alternator creates AC internally (not DC like a SG) and is then rectified by diodes which are almost always integral to the alternator. The alternator is usually a three phase device and will have 3 or 6 diodes for rectification. Alternators tend to be less than 150 amps, where SGs are typically 200 to 300 amp devices.
If the SG model is provided, perhaps a refined response is possible.


text:
How does the extension of inboard flaps raise the effective critical angle of attack of the outer wing?
I raised a question about this on this post in the comment section and was suggested by Peter Kämpf to create a new question. So here it goes: How does the extension of inboard flaps raise the effective critical angle of attack of the outer wing? And when that happens, why does the outer wing stall first without the help of slats when extension of the inboard flaps induces more lift on the whole wing, not just on the outer wing?

First it is beneficial to have an idea how the pressure field around an airfoil influences the flow around it. With powerful flaps, the suction peak on the upper side is already well developed at smaller angles of attack, so the surrounding air will be accelerated towards that low pressure area.
Now you need to extend that mental picture to 3D. The inner wing has those flaps deployed and, consequently, a suction peak near the leading edge and low pressure on the whole upper side. This will also suck in air from the side. As a consequence, the flow moving towards the outer wing will see a similar upward acceleration as does the flow streaming towards the inner wing, plus a sideways acceleration. This acceleration increases the local angle of attack at the leading edge of both wing sections. If the outer wing was already close to its stall angle of attack before the flaps were lowered, now the increased angle of attack will push the flow beyond the stall condition.
The geometrical angle of attack (measured as the angle between the flow direction at infinity and the reference length of the airfoil) did not change. The "real" angle of attack as experienced by the outer wing, however, will produce a flow similar to what would normally only be experienced at a higher geometrical angle of attack. This moves the outer wing into the stall region when the inner wing still works in the linear realm. This can lead to asymmetric stalls which produce a strong and sudden rolling moment, and at low altitude that is the last thing you need while lining up with the runway.
Adding slats will move the stall angle of attack up a few degrees, and now it will again be the inner wing which stalls first, as it should.

So is it a (additional) sideway acceleration into the inner wing from the outer wing that gives a greater effective angle of attack to the outer wing?

@lemonincider: The sideways component of acceleration is not causing the higher local angle of attack, but the vertical component is. The flow is different from that on the inner, flapped wing in that there is a sideways component and the vertical component decreases the farther you move to the tip.

@PeterKämpf you mention that as the outer wing moves into the stall region, asymmetric stalls can occur and strong rolling moments can result. If this same behavior occurs concurrently on both wings, what causes the rolling moment?

@Geoff: If both wingtips stall at the same time, no overall rolling moment will occur. But to bet that stall is every time symmetric is like playing Russian roulette. Sideslip or gusts can then quickly ruin your day.

@peterkampf that makes sense, a perfectly symmetric stall would be unlikely indeed. I just had to make sure I wasn’t missing something silly


text:
Are you cleared to next altitude when you get "direct" while flying SID?

Let's say you just took off from the TACOMA airport and were flying ATOME TWO DEP. ARRIE transition. The Seattle tower instructs you "direct to ZUMBI" and to contact Departure, and you contact Departure and report "Departure, N1234, passing 2000, direct ZUMBI." If departure just replies "N1234, Departure, Radar contact," are you cleared to the next altitude of KIMSH (at or above 10000ft) or should you maintain 9000 until Departure gives you higher?

What was your original clearance from Clearance Delivery or PDC? Climb Via? Climb and maintain XXX? Climb via except maintain XXX? Specify that, please.

@Ralph J The clearance was Climb Via

Given the clarification in the comment, that the initial clearance was to Climb Via the SID...
You’re still cleared climb via, even with the turn direct, so not above 9 until past ZUMBI, but as soon as you are past that fix, climb up to 15, making sure you’re at or above 10 at KIMSH.
To address some things in the comments for the other answer:
When you're cleared OFF of a SID or STAR that you'd been climbing/descending via, you're in a no-man's-land of ambiguity: can I immediately climb/descend unrestricted to the top/bottom altitude as published, or does the controller need me to stop at something prior to that altitude -- perhaps to maintain separation with other traffic?
In the case of the OP's question, you still have the (only) hold-down point in front of you: ZUMBI at 9.  There was nothing before that would keep you from climbing straight up to 9, so why stop any sooner than that after the direct?  And, after ZUMBI you'll still be on the SID routing, which gives you a climb to 15, so nothing changed there either.
As for what the controllers ought to be doing, maybe they need to give you an altitude clearance with every shortcut no matter how inconsequential, but if they don't there is no ambiguity in what the pilot still needs to be doing here.
Getting vectored off the procedure (or, potentially, a shortcut that bypasses ZUMBI) is an entirely different story: you absolutely need to query the controller if he doesn't state an altitude clearance in that case. If he needs you to go no higher than 9 until past the line of arrivals that cross the departure path near ZUMBI, he should make that clear. Or if nobody is on that arrival path & you're good to climb unrestricted right now, he should tell you that as well.  But in the OP's question as stated, this isn't ambiguous. The shortcut mentioned doesn't bypass, nor introduce, any altitude restrictions.

Do you have a reference for this?


text:
What does METAR show when actual RVR is below the reporting minimum?
RVR is measured between 50m and 1500m (ICAO). When the actual RVR is below 50m, what does METAR show?


text:
Why do some countries separate a transition level and a transition altitude?
The US airway system uses a single transition level (or altitude), but some other countries like China separate a transtion altitude and a transition level with the transition layer in between.
Could anybody kindly explain why they use this type of separate transition system? I can guess it's there to prevent possible mid-air collisions between two aircraft using two different altimeter settings (QNH and QNE) but I don't understand how exactly that works.

USA has a transition layer as well. It is 0 feet if the QNH is 1013,25 hPa, but in all other cases it is larger than that

@J. Hougaard You can call it a transition layer as well but that's a little different from the transition layer I'm talking about here in that it's between two different transition altitude and level, for example like the transition altitude being 14,000 and the transition level being FL160.

Related "3.9 Minimum usable flight levels" on VATEUD with this picture.

By definition, the transition level is the lowest usable flight level above the transition altitude. So if there is a transition altitude, there is a transition level.
In the USA, the transition altitude is 18 000ft. If the QNH (altimeter setting) is higher than 1013.25 mbar then the transition level is FL180. This provides at least 1000 ft separation from aircraft flying at 17 000 ft (or 500 ft from the VFR at 17 500 ft).
If the QNH is lower than 1013.25 mbar then the transition level is FL190 or even FL200 to ensure there is at least 1000 ft separation from 17 000 ft.
The transition level in other countries is based on similar logic.

The 'flexible' transition level makes maximum use of the airspace by using all available altitudes and flight levels. It appears from the question that some countries use a fixed transition level that accounts for the worst case QNH. It sacrifices airspace utilization for operational expediency. They don't have to check the barometric pressure to see if the boundary area levels are available for use as they're always excluded.

@ymb1 No more so than any other VFR altitude.  500 feet vertical separation is the standard between IFR and VFR below Class A airspace with IFR traffic assigned on the thousands and VFR 500 feet above or below.

When you say in the US "if the QNH is lower than 1013.25 mbar then the transition level is FL 910 or even FL 200," you mean the ATC instructs pilots to change their altimeter settings to the local QNH setting at FL 190 or FL 200 rather than at FL 180 for separation purposes?

It basically means that FL180 / FL190 do not exists under those conditions. Aircraft will not be cleared to those levels. ATC does not tell pilots at which altitudes they have to change their altimeter setting. Instead they clear / instruct the aircraft to a flight level or an altitude (+QNH). The altimeter setting is implied.

I think I was not fully understanding your point. I now get it. Thank you!